Some Properties of Glutamine Synthetase From the Nitrifying Bacterium Nitrosomonas Euro Paea

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Abstract
N. europaea oxidizes to nitrite, thereby deriving energy for growth. Glutamate dehydrogenase (NADP+) (EC 1.4.1.4) is the main route for the incorporation of ammonia into glutamic acid, because glutamate synthase (NADPH) (EC 1.4.1.13) was not detected in cell-free extracts of N. europaea. Some properties of a partially purified glutamine synthetase (EC 6.3.1.2) were determined, namely the effects of pH and metal ions, substrate requirements and and Ki values, based on biosynthetic and .gamma.-glutamyltransferase (EC 2.3.2.2) assays. The MW of the enzyme preparation was .apprx. 440,000. The .gamma.-glutamyltransferase activity was markedly inhibited by alanine, lysine, glutamic acid, aspartic acid and serine and to a lesser extent by glycine, asparagine, arginine and histidine. Except for tryptophan and cystine, the .gamma.-glutamyltransferase activity was inhibited to a greater extent by these amino acids than was the biosynthetic activity. Different pairs of amino acids in various combinations resulted in a cumulative inhibition of enzyme activity determined by either method. Of the various nucleotides tested, the .gamma.-glutamyltransferase activity of the enzyme was inhibited to a greater extent by di- and triphosphate nucleotides, IDP, CDP, UDP, ITP, CTP, TTP and ATP (except GDP and GTP), than by monophosphate nucleotides except AMP. Saturating concentrations of pyruvate, oxalate, oxaloacetate and .alpha.-ketoglutarate depressed enzyme activity. Various combinations of amino acids with adenine nucleotides exerted cumulative inhibitory effects on the transferase activity.